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In addition, however, changes in human activity since the middle of the 19th century have released C that occurred prior to 1955 mean that a single radiocarbon date may yield an imprecise calibrated age consisting of several possible age ranges.This difficulty may be overcome by obtaining a series of C dates from a sequence and either wiggle-matching these dates to a radiocarbon calibration curve or using additional information on dated materials and their surrounding environment to narrow the calibrated age ranges associated with each C levels between consecutive years offer the possibility of dating recent samples with a resolution of from one to a few years.The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died.The older a sample is, the less (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods occasionally permit accurate analysis of older samples.Genghis Khan paved the way for his grandson Kublai to become emperor of a united China and founder of the Yuan dynasty.In all, Genghis conquered almost four times the lands of Alexander the Great.From the most brutal beginning possible, Genghis survived to unite the Mongolian tribes and conquer territories as far apart as Afghanistan and northern China.

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Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years.

These approaches to dating the recent past are illustrated using examples from peats, lake and salt marsh sediments, tree rings, marine organisms and speleothems.

The method was developed by Willard Libby in the late 1940s and soon became a standard tool for archaeologists.

‘We found that during the short events such as the Black Death and the Ming Dynasty collapse, the forest re-growth wasn't enough to overcome the emissions from decaying material in the soil,’ explained Pongratz.

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‘But during the longer-lasting ones like the Mongol invasion...

But the bloody Mongol invasion, which lasted a century and a half and led to an empire that spanned 22 per cent of the Earth’s surface, immediately stood out for its longevity.